Can't make BGE to accept the string "\n" string in exptression to activate an actuator
CR is no printable character. The keyboard logger does not do anything with it (tested in 2.76).

Better use the  (measured by a separate keyboard sensor) as event to evaluate whatever the keyboard logging already measured.

Typically on such an event, you:


evaluate whatever was entered
clear the log buffer
process whatever the evaluation resulted on


This also means you do not need to evaluate while entering the string (but you still can).

Here is a demo:


logging: logs printable keyboard input to property "Text"

evaluate: input confirmed on CR

help: evaluate if "help" was entered 

toggle help: send a message "toggle help" when help was requested

reset input: clears the input field, allowing to enter a new phrase

I hope it helps